Re: [PATCH 2/2] accel/tcg: interrupt/exception handling uses bql_interrupt flag

[Paolo Bonzini <pbonzini@redhat.com>]

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Yes, that is correct. It's more work but also more maintainable.

Thanks,

Paolo

Il ven 31 lug 2020, 22:09 Robert Foley <robert.foley@linaro.org> ha scritto:

> On Fri, 31 Jul 2020 at 14:02, Paolo Bonzini <pbonzini@redhat.com> wrote:
> >
> > On 31/07/20 14:51, Robert Foley wrote:
> > > This change removes the implied BQL from the cpu_handle_interrupt,
> > > and cpu_handle_exception paths. We can now select per-arch if
> > > the BQL is needed or not by using the bql_interrupt flag.
> > > By default, the core code holds the BQL.
> > > One benefit of this change is that it leaves it up to the arch
> > > to make the change to remove BQL when it makes sense.
> > >
> > > Signed-off-by: Robert Foley <robert.foley@linaro.org>
> >
> > No, please just modify all implementation to do lock/unlock.  It's a
> > simpler patch than this on.
>
> Sure, we will update the patch based on this.
>
> To clarify, the suggestion here is to remove the bql_interrupt flag
> that we added and change all the per-arch interrupt callback code to
> do the lock/unlock of the BQL?  So for example change
> x86_cpu_exec_interrupt, and arm_cpu_exec_interrupt, etc to lock/unlock BQL?
>
> Thanks,
> -Rob
>
>
> >
> > Paolo
> >
> > > ---
> > >  accel/tcg/cpu-exec.c | 34 ++++++++++++++++++++++++++--------
> > >  1 file changed, 26 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c
> > > index 80d0e649b2..cde27ee0bf 100644
> > > --- a/accel/tcg/cpu-exec.c
> > > +++ b/accel/tcg/cpu-exec.c
> > > @@ -517,9 +517,13 @@ static inline bool cpu_handle_exception(CPUState
> *cpu, int *ret)
> > >  #else
> > >          if (replay_exception()) {
> > >              CPUClass *cc = CPU_GET_CLASS(cpu);
> > > -            qemu_mutex_lock_iothread();
> > > +            if (cc->bql_interrupt) {
> > > +                qemu_mutex_lock_iothread();
> > > +            }
> > >              cc->do_interrupt(cpu);
> > > -            qemu_mutex_unlock_iothread();
> > > +            if (cc->bql_interrupt) {
> > > +                qemu_mutex_unlock_iothread();
> > > +            }
> > >              cpu->exception_index = -1;
> > >
> > >              if (unlikely(cpu->singlestep_enabled)) {
> > > @@ -558,7 +562,7 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >      if (unlikely(cpu_interrupt_request(cpu))) {
> > >          int interrupt_request;
> > >
> > > -        qemu_mutex_lock_iothread();
> > > +        cpu_mutex_lock(cpu);
> > >          interrupt_request = cpu_interrupt_request(cpu);
> > >          if (unlikely(cpu->singlestep_enabled & SSTEP_NOIRQ)) {
> > >              /* Mask out external interrupts for this step. */
> > > @@ -567,7 +571,7 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >          if (interrupt_request & CPU_INTERRUPT_DEBUG) {
> > >              cpu_reset_interrupt(cpu, CPU_INTERRUPT_DEBUG);
> > >              cpu->exception_index = EXCP_DEBUG;
> > > -            qemu_mutex_unlock_iothread();
> > > +            cpu_mutex_unlock(cpu);
> > >              return true;
> > >          }
> > >          if (replay_mode == REPLAY_MODE_PLAY &&
> !replay_has_interrupt()) {
> > > @@ -577,13 +581,15 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >              cpu_reset_interrupt(cpu, CPU_INTERRUPT_HALT);
> > >              cpu_halted_set(cpu, 1);
> > >              cpu->exception_index = EXCP_HLT;
> > > -            qemu_mutex_unlock_iothread();
> > > +            cpu_mutex_unlock(cpu);
> > >              return true;
> > >          }
> > >  #if defined(TARGET_I386)
> > >          else if (interrupt_request & CPU_INTERRUPT_INIT) {
> > >              X86CPU *x86_cpu = X86_CPU(cpu);
> > >              CPUArchState *env = &x86_cpu->env;
> > > +            cpu_mutex_unlock(cpu);
> > > +            qemu_mutex_lock_iothread();
> > >              replay_interrupt();
> > >              cpu_svm_check_intercept_param(env, SVM_EXIT_INIT, 0, 0);
> > >              do_cpu_init(x86_cpu);
> > > @@ -595,7 +601,7 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >          else if (interrupt_request & CPU_INTERRUPT_RESET) {
> > >              replay_interrupt();
> > >              cpu_reset(cpu);
> > > -            qemu_mutex_unlock_iothread();
> > > +            cpu_mutex_unlock(cpu);
> > >              return true;
> > >          }
> > >  #endif
> > > @@ -604,7 +610,15 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >             True when it is, and we should restart on a new TB,
> > >             and via longjmp via cpu_loop_exit.  */
> > >          else {
> > > +            cpu_mutex_unlock(cpu);
> > > +            if (cc->bql_interrupt) {
> > > +                qemu_mutex_lock_iothread();
> > > +            }
> > >              if (cc->cpu_exec_interrupt(cpu, interrupt_request)) {
> > > +                if (cc->bql_interrupt) {
> > > +                    qemu_mutex_unlock_iothread();
> > > +                }
> > > +                cpu_mutex_lock(cpu);
> > >                  replay_interrupt();
> > >                  /*
> > >                   * After processing the interrupt, ensure an
> EXCP_DEBUG is
> > > @@ -614,6 +628,11 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >                  cpu->exception_index =
> > >                      (cpu->singlestep_enabled ? EXCP_DEBUG : -1);
> > >                  *last_tb = NULL;
> > > +            } else {
> > > +                if (cc->bql_interrupt) {
> > > +                    qemu_mutex_unlock_iothread();
> > > +                }
> > > +                cpu_mutex_lock(cpu);
> > >              }
> > >              /* The target hook may have updated the
> 'cpu->interrupt_request';
> > >               * reload the 'interrupt_request' value */
> > > @@ -627,7 +646,7 @@ static inline bool cpu_handle_interrupt(CPUState
> *cpu,
> > >          }
> > >
> > >          /* If we exit via cpu_loop_exit/longjmp it is reset in
> cpu_exec */
> > > -        qemu_mutex_unlock_iothread();
> > > +        cpu_mutex_unlock(cpu);
> > >      }
> > >
> > >      /* Finally, check if we need to exit to the main loop.  */
> > > @@ -691,7 +710,6 @@ static inline void cpu_loop_exec_tb(CPUState *cpu,
> TranslationBlock *tb,
> > >      }
> > >  #endif
> > >  }
> > > -
> > >  /* main execution loop */
> > >
> > >  int cpu_exec(CPUState *cpu)
> > >
> >
>
>

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